Choose the right grammatical form in each gap to complete the text

I have never thought about the idea of a working holiday. I used to like going to a hot country, having rest and lots of fun on the beach or somewhere else. I thought that [a|an|the|] holiday is a time only for yourself, for being selfish!But once something had happened that completely changed my mind. I heard a story of my classmate about how she went to the countryside to clean up the river. A group of [a|an|the|] people spent three weeks collecting the rubbish on [a|an|the|] bank of the local river. And she was so happy and proud of herself.

And I thought, "Why don't I do the same? I can make a difference too!" I could go to [a|an|the|] African country to teach [a|an|the|] poor English, or help with houses or pipeline construction, or whatever! How many good things I could do if I devoted my spare time in the right way!